The present invention relates generally to seals, and more particularly, to seals of the so-called torsional deflection type which are adapted to exclude grit from a sealed area and retain oil, grease, or other lubricant therein.
Seals made according to the present invention are particularly adapted for use in severe service environments where the relative motion between the two sealed parts comprises an oscillatory motion only of a relatively limited angular extent. In this respect, the seals are distinguished from seals wherein the sealed parts undergo one or more complete rotations relative to each other.
One advantage of torsional deflection type seals is that they make possible the retention of oil or the like within a sealed cavity without the need for two surfaces which undergo motion relative to each other. In other types of seals, oil will escape between these surfaces if they lack the requisite pressure to maintain the seal, or if they move apart for any reason. A common type of torsional deflection seal, however, uses a cylinder or similar annulus or an elastomeric material such as natural or synthetic rubber instead of two movable surfaces. This member is bonded or otherwise firmly affixed to a pair of rigid members, usually metal or the like, each of which is attached to a separate, relatively movable member.
Accordingly, in a typical torsional deflection seal, a snug secondary seal is made between one sealed part and one metal ring or the like, and a similar, snug, secondary or non-rotational seal is established between the other sealed part and the other metal ring. When the sealed parts oscillate relative to each other, the cylinder undergoes a torsional deflection action, that is, one axial end thereof rotates circumferentially relative to the other axial end, with the body of the cylinder or annulus taking the deflection by reason of its inherent elasticity.
Consequently, in seals of this type, there actually is no so-called primary seal or relative interfacial motion of elements of the seal itself, but merely two so-called secondary seals, that is, static seals at points where there is no relative rotation between the part of the seal and the other sealed part. Consequently, if the secondary seals are properly installed, there is no possibility of leakage as long as the annulus itself remains intact and bonded to the members which are installed in the relatively movable parts.
However, in torsional deflection seals of the prior art, the act of snugly fitting the metal or other bonded elements to the movable part created a problem in that, were the sealed parts ever to undergo deflection in excess of a predetermined, permitted angle, permanent damage would be done to the seal, either by way of causing the seal to take a "set" or loss of elasticity, or, in extreme cases, with failure resulting from exceeding permissible shear stresses.
Referring now to the background of the invention, it is common in the track laying vehicle industry to manufacture the track assemblies themselves in a certain location or facility, and thereupon to store these tracks until it is time for installation thereof on a vehicle. In some cases, the completed and assembled tracks are merely kept in storage for a reasonable period of time, but in other cases, the track assemblies are shipped to another location, which in some cases, is in another country, for ultimate installation on the vehicle.
During the handling which is attendant to storage and shipping, the track pins or other sealed parts are sometimes called upon to undergo torsional deflection through an angle much greater than the specified or permitted angle. In other words, if the chain is folded back upon itself, the links of the chain may undergo deflection of 40.degree. to 55.degree., while in normal use, the track links would undergo an angular deviation of perhaps 20.degree. to 35.degree., usually 27.degree. to 32.degree., as the links are successively wrapped around, and then straightened from a drive sprocket or roller.
Accordingly, with prior art seals, there has been a problem of storage, shipping or transient handling of chains in which the links are permitted to only undergo limited angular deflection with respect to one another. In such cases, torsional deflection type seals were not used. In other cases, the chains required special handling or storage, which often constituted a significant disadvantage. In other words, if a chain could never be coiled for storage in a form requiring the links to exceed a given deflection angle, such as 15.degree., for example, the space required to store the chain would be excessive and would create handling problems which might, in effect, rule out the adoption of an otherwise desirable torsional deflection type seal.
Accordingly, it is an object of the present invention to provide an improved torsional deflection type track pin seal.
Another object of the invention is to provide a track pin seal which includes a pair of end members adapted to be received within portions respectively of a pair of sealed parts and to remain fixed relative to such parts under normal use, but which, under extreme conditions, may rotate relative thereto so as to avoid imposing undue strain on the elastomeric components of the seal.
Yet another object is to provide a torsional deflection type seal which, by its design, inherently limits the amount of torque or the effective angle which can be imposed upon the cylinder, annulus or other elastomeric part.
A still further object of the invention is to provide a sealed vehicle track having a plurality of seals of the improved type.
Another object of the invention is to provide a seal having a pair of end parts and an elastomeric annulus extending therebetween, with the end parts being constructed and arranged so that in normal use they do not engage each other, but when a predetermined limit of free movement is exceeded, one end part engages the other end part and causes it to rotate relative to the sealed part within which it is received.
A still further object is to provide a torsional deflection type track pin seal having driving and driven elements adapted only for intermittent engagement when angular deflection between the two sealed parts exceeds a predetermined degree.
Another object is to provide a track pin seal having first and second end caps, a generally cylindrically, axially extending, elastomeric torsional deflection element and disposed between said ends, with said two ends having means thereon for cooperative engagement after a predetermined angle of relatively free movement between such parts has occurred.
Another object is to provide a seal unit which includes a casing with a driving flange and a casing with one or more driven flanges, with the driven and driving flanges being spaced circumferentially apart from each other and being adapted for radial or axial engagement with each other after a permitted amount of free play between the units has occurred in use.
The foregoing and other objects and advantages of the invention are achieved by providing a seal unit having first and second members adapted to engage, respectively, first and second sealed parts, torsionally deflectable means joining the first and second members, with the first and second members respectively having cooperating means thereon for engaging each other after a predetermined amount of free movement between them has taken place with at least one of said end members being constructed and arranged to permit movement relative to the part with which they are associated in use, whereby, the end parts do not engage each other during limited oscillation, but upon engagement, cause the driven end part to rotate relative to one of the sealed parts.
The exact manner in which these and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the accompanying drawings showing the preferred embodiments of the invention, and in which like reference numerals indicate corresponding parts throughout the several figures.